Damped turbomachine rotor assembly

ABSTRACT

The disclosure illustrates a centrifugal compressor comprising an inducer hub telescoped over an adjacent shoulder of an impeller hub. A nut threaded on the impeller hub maintains the inducer hub, an intermediate annular resilient ring and the impeller hub in abutment with sufficient pressure to damp vibrations in the rotor assembly.

United States Patent Cronstedt [4 1 July 18, 1972 [54] DAMPEDTURBOMACHINE ROTOR 3,065,954 1 H1962 Whitaker ..4 1 6/500 ASSEMBLY2,664,240 12/1953 06mm ..4l6/5OO 72] Inventor: Val Cronstedt,Williamsport, Pa. FOREIGN PATENTS OR APPLICATIONS Assigneer AvcoCorporation, williamsport, 604,730 7/1948 Great Britain .416/244 [22]Filed: Oct. 1, 1970 Primary Exa'miner-Everette A. Powell, Jr. PP NW ,146Assistant Examiner--Clemens Schmilkowksi Attorney-Charles M. Hogan andGary (iron [52] U.S. Cl.... ..4l6/l83, 416/244, 416/500 [51] Int. Cl..F0ld 5/26 ABSTRACT [58] held Search "416/ 500; 415/] 19 The disclosureillustrates a centrifugal compressor comprising an inducer hubtelescoped over an adjacent shoulder of an im- [56] References Citedpeller hub. A nut threaded on the impeller hub maintains the UNITEDSTATES PATENTS inducer hub, an intermediate annular resilient ring andthe impeller hub in abutment with sufiiciemt pressure to damp vibralNewland l tions in the rotor assembly 2,405,283 8/1946 Birmann ..4l6/5OO2,941,780 6/1960 Von Der Nuell et a1, ..416/500 4 Claim, 2 DrawingFigures Patented July 18, 1972 INVENTOR VAL CROMSTEDT BY M 77/. g?ATTORNEYS.

DAMPED TURBOMACHINE ROTOR ASSEMBLY The present invention relates toturbomachine rotor assemblies and more particularly assemblies of thetype that have provision for damping vibrations.

In the gas turbine art there are numerous devices and approaches tominimize vibration in rotor assemblies. These devices are necessarybecause the blades in the rotor assembly will vibrate at their naturalfrequencies with sufficient amplitude to impair their structuralintegrity.

One type of damping arrangement for this purpose consists of elementsformed on one set of blades to rub against adjacent blades andfrictionally damp vibrations. While this approach is generallyeffective, it is expensive to manufacture a rotor that utilizes thistype of damping and, in addition, it creates aerodynamic disturbanceswhich may lead to loss of efficiency.

Another approach that has been used may be found in the U. S. Pat. toBirrnann, No. 2,405,283, wherein a shoulder adjacent the inner portionsof one set of blades is machined away so that only the outer portions ofthe blades abut adjacent blades. The two hubs that support the bladesare held with sufficient axial force to cause the edges of the blades tofrictionally engage and damp vibrations. This approach again iseffective but it is expensive to manufacture the shoulder and machinethe abutting surfaces of the individual blades.

Accordingly, the object of the present invention is to provide a highlyefficient and economical means for damping a turbomachine rotor.

The above end is achieved by a damped turbomachine rotor assemblycomprising first and second bladed annular hubs that have an annularenergy absorbing ring positioned between them. This ring and the hubsare maintained in abutment with sufficient axial pressure to dampvibrations in the rotor assembly.

The above and other related objects and features of the presentinvention will be apparent from a reading of the description and a studyof the accompanying drawing and the novelty thereof pointed out in theappended claims.

In the drawing:

FIG. 1 is a longitudinal sectional view of a centrifugal compressorrotor assembly embodying the .present invention;

FIG. 2 is a view taken on lines 22 of FIG. 1 which shows the fundamentalmode of vibration of the compressor hub.

Referring now to FIG. 1 there is shown a centrifugal compressor rotorassembly with which the present invention may be used. The rotorassembly comprises a first generally annularly shaped hub 12 spacedoutwardly from its axis of rotation A. The hub 12 has a series ofradially extending blades 14 to form the impeller portion of the rotorassembly 10. A second hub 16 is positioned upstream of the hub 12 and isalso annular and spaced outwardly from the axis of rotation A. Hub 16has a series of inducer blades 18 which extend radially outward but arecambered so as to efficiently receive air from an axially directedinlet, shown in phantom and designated by reference character 21. Theinducer blades 18 correspond with the impeller blades 14 to form agenerally annular accelerating flow across the centrifugal compressorrotor 10. i

A resilient annular ring 22 is positioned in a groove 24 in hub 12 andprojects from axial shoulder so that the ring 22 maintains hub 16 andits corresponding blades out of contact with hub 12 and itscorresponding blades 14 (shown in exaggerated scale). Hub 12 has anelongated shaft portion 26 over which hub 16 is telescoped. A pilotdiameter 28 on the elongated shaft portion 26 and a correspondingdiameter 30 on the inducer hub 16 centers it on elongated shaft portion26 of hub 12. An internally threaded element 32 is screwed onto thethreaded portion 34 of the elongated portion 26 by a suitable tool whichengages slots 34 in element 32. Element 32 holds the inducer hub,resilient ring 22 and the impeller hub 12 in abutment. The threadedelement 32 is tightened to hold the elements together with sufficientaxial force to damp vibrations as described below.

In operation, the centrifugal compressor rotor assembly 10 rotates at ahigh rate of speed. Due to many exciting forces the blade 18 and 14 tendto vibrate in their several modes. As shown in FIG. 2, the resultantvibration causes deformation of the annular inducer hub 16 from whichthe blades 18 extend radially. The deflection of the hub for a swing ofblades 18 to the left is shown in exaggerated proportion by the phantomlines of FIG. 2. It can be seen that this deflection generally resemblesa sine wave superimposed on the annular shape of the hub. A swing of theblades to the right causes a similar deflection in the oppositedirection.

With the resilient ring 22 in abutment between the hubs l6 and 12, thetendency toward this type of deflection causes a frictional rubbingbetween the ring and the adjacent hubs. This damps the vibration of theblades by absorbing energy created by the deflection of the root of theblades. However, the close coupling of the hubs enables sufficientenergy to be absorbed adequately to damp vibrations.

There are a number of resilient materials which may be suitable for thispurpose. One type would be fiber and another material would be rubber.It is pointed out that temperature considerations for the rotorinfluence the selection of the material to be used. For highertemperatures it is necessary to utilize a temperature resistantmaterial.

While the present invention has been described in connection with acentrifugal compressor, it is believed that those skilled in the art canadapt the invention to other turbomachine rotors, such as axial flowtypes or a centripetal turbine assembly, without departing from thespirit of the present invention. Accordingly, its scope is to bedetermined solely by the appended claims.

Having thus described the invention, what is claimed as novel anddesired to be secured by Letters Patent of the United States is:

l. A damped turbomachine rotor assembly comprising:

a first annular hub spaced from its axis of rotation;

a plurality of blades extending generally radially from said a secondbladed annular hub outwardly spaced from its axis of rotation;

a plurality of blades extending generally radially from said second huband corresponding with the blades on said first hub to form a generallyannular flow path across said rotor assembly, one of said hubs having arecess for retaining said ring within the periphery of said hubs;

an annular resilient ring positioned between said first and second hubs;and

means for maintaining said ring and hubs in abutment with sufficientpressure to damp vibrations in said rotor assembly.

2. A rotor assembly as in claim 1 wherein:

said first hub further comprises an elongated axially extending shaftportion;

said second hub is telescoped over the elongated shaft portion of theother hub; and

the means for maintaining said disks and hubs in abutment comprises anelement secured to the elongated shaft portion of said first hub.

3. A rotor assembly as in claim 2 wherein said hub is an inducer hub andsaid first hub is an impeller hub, whereby said rotor assembly comprisesa centrifugal compressor.

4. A rotor assembly as in claim 3 wherein said inducer is telescopedover said impeller and said abutment maintaining means comprises asleeve element threaded over said elongated shaft portion of saidimpeller hub for holding said disks and hubs in abutment.

T3 33 UNlTED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,677,663 D d July 18, 1972 Inv9nt0r( VAL CRONSTEDT It is certified thaterror appears in the above identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 6, "blade" should read "blades" Column 2, lines 47-50should read as follows:

"rotor assembly;

an annular resilient ring positioned between said first and second hubs,one of said hubs having a recess for retaining said ring within theperiphery of said hubs; and" Signed and sealed this ZLLth day of October1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. A damped turbomachine rotor assembly comprising: a first annular hubspaced from its axis of rotation; a plurality of blades extendinggenerally radially from said first hub; a second bladed annular huboutwardly spaced from its axis of rotation; a plurality of bladesextending generally radially from said second hub and corresponding withthe blades on said first hub to form a generally annular flow pathacross said rotor assembly, one of said hubs having a recess forretaining said ring within the periphery of said hubs; an annularresilient ring positioned between said first and second hubs; and meansfor maintaining said ring and hubs in abutment with sufficient pressureto damp vibrations in said rotor assembly.
 2. A rotor assembly as inclaim 1 wherein: said first hub further comprises an elongated axiallyextending shaft portion; said second hub is telescoped over theelongated shaft portion of the other hub; and the means for maintainingsaid disks and hubs in abutment comprises an element secureD to theelongated shaft portion of said first hub.
 3. A rotor assembly as inclaim 2 wherein said hub is an inducer hub and said first hub is animpeller hub, whereby said rotor assembly comprises a centrifugalcompressor.
 4. A rotor assembly as in claim 3 wherein said inducer istelescoped over said impeller and said abutment maintaining meanscomprises a sleeve element threaded over said elongated shaft portion ofsaid impeller hub for holding said disks and hubs in abutment.